The Atacama Desert is the driest in the world.
Why it is true
The Atacama Desert in Chile is the driest non-polar desert in the world. Some weather stations in the region have never recorded rain since measurements began, and relative humidity can be below 10 percent.
Source: USGS
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This is the reading side of the site, so the answer is in the sentence above — that is the whole point of it. Test yourself works the other way round: the question comes on its own, and the fact and the explanation only appear once you have answered.